I
n the previous chapter, you have
learnt how animals reproduce. It is
only after ‘growing up’ to a certain
age that human beings and many other
animals can reproduce. Why can
humans reproduce only after a certain
age?
In this chapter, you will learn about
changes that take place in the human
body after which a person becomes
capable of reproduction.
In Chapter
6,
you
have learnt about
human reproductive organs. Here, we
shall discuss the role that hormones play
in bringing about changes that make a
child grow into an adult.
7.1 Adolescence and Puberty
Boojho was celebrating his 12th
birthday. After his friends left, Boojho
and Paheli began chatting with their
parents. Paheli studies in an all-girls
school. She started laughing. She
remarked that many of Boojho’s school
friends, whom she met after a year, had
suddenly shot up in height. Some of
them were looking very funny with a
hairy line above their lips. Her mother
explained that the boys had grown up.
Growth begins from the day one is
born. But upon crossing the age of 10
or 11, there is a sudden spurt in growth
which becomes noticeable. The changes
taking place in the body are part of
growing up. They indicate that you are
I wonder how long this
period marked by changes
in the body will last!
no longer a child but are on the way to
becoming an adult.
It is a strange period of life
when you are neither a child nor
an adult. I wonder whether this
period between childhood and
adulthood had a special name!
Growing up is a natural process. The
period of life, when the body undergoes
changes, leading to reproductive
maturity, is called adolescence.
Adolescence begins around the age of
11 and lasts upto 18 or 19 years of age.
Since this period covers the ‘teens’ (13
to 18 or 19 years of age), adolescents
are also called ‘teenagers’. In girls,
adolescence may begin a year or two
earlier than in boys. Also, the period of
adolescence varies from person to person.
The human body undergoes several
changes during adolescence. These
changes mark the onset of puberty. The
most important change which marks
puberty is that boys and girls become
capable of reproduction. Puberty ends
when an adolescent reaches reproductive
maturity.
R
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R
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% of full height
Boys Girls
8 72%
77%
9 75%
81%
10 78% 84%
11 81% 88%
12 84% 91%
13 88% 95%
14 92% 98%
15 95% 99%
16 98% 99.5%
17 99% 100%
18 100% 100%
Age in
Years
Paheli and Boojho
realised that sudden
increase in height and
hairy line above the lips
in boys were signs of
adolescence. They
wanted to know more
about other changes at
puberty.
7.2 Changes at Puberty
Increase in Height
The most conspicuous change during
puberty is the sudden increase in
height. At this time the long bones, that
is, the bones of the arms and the legs
elongate and make a person tall.
Activity 7.1
The following chart gives the
average rate of growth in height of
boys and girls with age. The figures
in columns 2 and 3, give the
percentage of the height a person
has reached at the age given in
column 1. For example, by the age
11, a boy has reached 81% of his
probable full height, while a girl
has reached 88% of her full
height. These figures are only
representative and there may be
individual variations.
Use the Table for your friends
and work out how tall they are likely
to be. Find out who is likely to be
Calculation for full height (cm)
( )
100
Present height cm
% of full height at this age
×
(as given in the chart)
Example:
A boy is 9 years old and 120 cm
tall. At the end of the growth period
he is likely to be
×
120
100
75
cm = 160 cm tall
the tallest and who might be the
shortest in your class.
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There is no need for Paheli to worry.
All parts of the body do not grow at the
same rate. Sometimes the arms and legs
or hands and feet of adolescents look
oversized and out of proportion with the
body. But soon the other parts catch
up and result in a proportionate body.
You must have noticed that height
of an individual is more or less similar
to that of some family member. This is
because height depends on the genes
inherited from parents. It is, however,
very important to eat the right kind of
food during these growing years. This
helps the bones, muscles and other
parts of the body get adequate
nourishment for growth. You will find
nutritional needs of adolescents
discussed later in the lesson.
Change in Body Shape
Have you noticed that boys in your class
have broader shoulders and wider chests
than boys in junior classes? This is
because they have entered the age of
puberty when shoulders generally
broaden as a result of growth. In girls,
the region below the waist becomes
wider.
In boys, the muscles of the body grow
more prominently than in the girls.
Thus, changes occurring in adolescent
boys and girls are different.
Voice Change
Did you notice that sometimes the voice
of some of the boys in your class cracks?
At puberty, the voice box or the larynx
begins to grow. Boys develop larger voice
boxes. The growing voice box in boys can
be seen as a protruding part of the throat
Activity 7.2
Use the data given in Activity 7.1 to
draw a graph. Take age on the
X-axis and per cent growth in height
on the Y-axis. Highlight the point
representing your age on the graph.
Find out the percentage of height
you have already reached. Calculate
the height you might eventually
reach. Tally your graph with the one
given here (Fig. 7.1).
Fig. 7.1 : Graph showing percentage of height
with age
I am worried. Though I
have become taller, my
face looks much smaller
compared to my body.
Initially, girls grow faster than boys
but by about 18 years of age, both reach
their maximum height. The rate of
growth in height varies in different
individuals. Some may grow suddenly
at puberty and then slow down, while
others may grow gradually.
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and pimples on the face at this time
because of the increased activity of these
glands in the skin.
Development of Sex Organs
Look up Fig. 6.1 and 6.3 of the
previous lesson which show sex
organs of humans. At puberty, male
sex organs like the testes and penis
develop completely. The testes also
begin to produce sperms. In girls, the
ovaries enlarge and eggs begin to
mature. Also ovaries start releasing
mature eggs.
Reaching Mental, Intellectual and
Emotional Maturity
Adolescence is also a period of change
in a person’s way of thinking.
Adolescents are more independent than
before and are also self conscious.
Intellectual development takes place and
they tend to spend considerable time
thinking. In fact, it is often the time in
one’s life when the brain has the
greatest capacity for learning.
Sometimes, however, an adolescent may
feel insecure while trying to adjust to
the changes in the body and mind. But
as adolescent learners, you should know
that there is no reason to feel insecure.
These changes are a natural part of
growing up.
7.3 Secondary Sexual
Characters
You have learnt in Chapter 6, that
testes and ovaries are the reproductive
organs. They produce the gametes,
that is, sperms and ova. In girls,
breasts begin to develop at puberty
Many of my classmates
have a hoarse voice. Now I
know why?
Fig. 7.2 : Adam’s apple in a grown up boy
called Adam’s apple (Fig. 7.2). In girls,
the larynx is hardly visible from the
outside because of its small size.
Generally, girls have a high pitched voice,
whereas boys have a deep voice. In
adolescent boys, sometimes, the muscles
of the growing voice box go out of control
and the voice becomes hoarse. This state
may remain for a few days or weeks after
which the voice becomes normal.
A few glands such as sweat glands,
oil glands and salivary glands release
their secretions through ducts.
Endocrine glands release hormones
directly into the bloodstream. So, they
are also termed ductless glands.
Increased Activity of Sweat and
Sebaceous Glands
During puberty the secretion of sweat
glands and sebaceous glands (oil glands)
increases. Many young people get acne
Adam’s
apple
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and boys begin to grow facial hair, that
is, moustaches and beard. As these
features help to distinguish the male
from the female they are called
secondary sexual characters. Boys
also develop hair on their chest. In
both, boys and girls, hair grows under
the arms and in the region above the
thighs or the pubic region.
Paheli and Boojho have now
understood that puberty marks the
beginning of the reproductive period
when one becomes capable of
reproduction. But they want to know
if reproductive life, once begun,
continues, or it ends some time.
The testes and ovaries secrete sex
hormones. You have just learnt that
these hormones are responsible for the
male and female secondary sexual
characters. Further, the sex hormones
are under the control of hormones from
the pituitary gland (Fig. 7.3). The
pituitary secretes many hormones, one
of which makes ova mature in the
ovaries and sperms form in the testes.
Both Boojho and Paheli wish to know
what initiates changes at puberty.
Fig. 7.3 : The onset of puberty is controlled by
hormones
The changes which occur at
adolescence are controlled by
hormones. Hormones are chemical
substances. These are secretions from
endocrine glands, or endocrine system.
The male hormone or testosterone
begins to be released by the testes at
the onset of puberty. This causes
changes in boys about which you have
just learnt, for example, the growth of
facial hair. Once puberty is reached in
girls, ovaries begin to produce the female
hormone
or estrogen which makes the
breasts develop. Milk secreting glands
or mammary glands develop inside the
breasts. The production of these
hormones is under the control of
another hormone secreted from an
endocrine gland called pituitary gland.
7.4 Role of Hormones in
Initiating Reproductive
Function
Endocrine glands release hormones
into the bloodstream to reach a
particular body part called target site.
The target site responds to the
hormone. There are many endocrine
glands or ductless glands in the body.
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7.5 Reproductive Phase of
Life in Humans
Adolescents become capable of
reproduction when their testes and
ovaries begin to produce gametes. The
capacity for maturation and production
of gametes lasts for a much longer time
in males than in females.
In females, the reproductive phase of
life begins at puberty (10 to 12 years of
age) and generally lasts till the age of
approximately 45 to 50 years. The ova
begin to mature with the onset of
puberty. One ovum matures and is
released by one of the ovaries once in
about 28 to 30 days. During this
period, the wall of the uterus becomes
thick so as to receive the egg, in case
it is fertilised and begins to develop.
This results in pregnancy. If
fertilisation does not occur, the
released egg, and the thickened lining
of the uterus along with its blood
vessels are shed off. This causes
bleeding in women which is called
menstruation. Menstruation occurs
once in about 28 to 30 days. The first
menstrual flow begins at puberty and
is termed menarche. At 45 to 50 years
of age, the menstrual cycle stops.
Stoppage of menstruation is termed
menopause. Initially, menstrual cycle
may be irregular. It take some time to
become regular.
Menstrual cycle is controlled by
hormones. The cycle includes the
maturation of the egg, its release,
thickening of uterine wall and its
breakdown if pregnancy does not
occur. In case the egg is fertilised it
begins to divide and then gets
embedded in the uterus for further
development as you have learnt in
Chapter 6 (Fig. 6.8).
7.6 How is the Sex of the
Baby Determined?
I heard my mother and my
aunt talking about my cousin
who is going to have a baby.
They were discussing whether
she would give birth to a boy
or a girl. I wonder what makes
the fertilised egg develop
either into a boy or a girl!
Paheli says that the
reproductive life of a
woman lasts from
menarche to menopause.
Is she right?
Boy or Girl?
Inside the fertilised egg or zygote is the
instruction for determining the sex of
the baby. This instruction is present in
the thread-like structures, called
chromosomes in the fertilised egg.
Chromosomes are present inside the
nucleus of every cell. All human beings
have 23 pairs of chromosomes in the
nuclei of their cells. Two chromosomes
out of these are the sex chromosomes,
named X and Y. A female has two X
chromosomes, while a male has one X
and one Y chromosome. The gametes
(egg and sperm) have only one set of
chromosomes. The unfertilised egg
always has one X chromosome. But
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sperms are of two kinds. One kind has
an X chromosome, and the other kind
has a Y chromosome.
See Fig. 7.4. When a sperm
containing X chromosome fertilises the
egg, the zygote would have two X
chromosomes and develop into a female
child. If the sperm contributes a Y
chromosome to the egg (ovum) at
fertilisation, the zygote would develop
into a male child.
and ovaries to produce their hormones.
You have already learnt that the
pituitary gland is an endocrine gland.
It is attached to the brain.
Apart from the pituitary, the testes
and the ovaries, there are other
endocrine glands in the body such as
thyroid, pancreas and adrenals
(Fig. 7.5).
Fig. 7.4 : Sex determination in humans
boy
girl
sperms
eggs
Now you know that the sex
chromosomes of the father determine the
sex of an unborn baby. The belief that
the mother is responsible for the sex of
her baby is completely wrong and to
blame her for this is totally unjustified.
7.7 Hormones other than
Sex Hormones
Look at Fig. 7.3 again. The hormones
secreted by the pituitary stimulate testes
Fig. 7.5 : Position of endocrine glands in the
human body
pituitary
gland
thyroid gland
adrenal
gland
pancreas
testis
position of
the ovary in
the female
Boojho and Paheli had once visited
their aunt who was a doctor and
remembered that a boy named Kaka had
a very big and bulging throat. Their aunt
had told them that Kaka was suffering
from ‘goitre’, a disease of the thyroid
gland. Kaka’s thyroid gland was not
producing the hormone thyroxine.
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Their aunt also told them that their
uncle was suffering from ‘diabetes’
because his pancreas was not producing
the hormone insulin in sufficient
quantities. Boojho and Paheli then
asked their aunt about the adrenal
glands, which are also shown in the
chart hung on the wall of her clinic. The
aunt told them that adrenal glands
secrete hormones which maintain the
correct salt balance in the blood.
Adrenals also produce the hormone
adrenalin. It helps the body to adjust
to stress when one is very angry,
embarrassed or worried.
Thyroid and adrenals secrete their
hormones when they receive orders from
the pituitary through its hormones.
Pituitary also secretes growth hormone
which is necessary for the normal
growth of a person.
controlled by insect hormones. In a
frog, it is controlled by thyroxine, the
hormone produced by thyroid.
Thyroxine production requires the
presence of iodine in water. If the water
in which the tadpoles are growing does
not contain sufficient iodine, the
tadpoles cannot become adults.
7.8 Role of Hormones in
Completing the Life
History of Insects and
Frogs
You have already learnt about the life
cycle of the frog. The tadpole passes
through certain stages to become a frog
(Chapter 6). This change from larva to
adult is called metamorphosis
(Fig. 6.10). Metamorphosis in insects is
Collect information from magazines
or from doctors and prepare a note
on the importance of consuming
iodised salt. You can also look for
this information on the internet.
7.9 Reproductive Health
The physical and mental well being of
an individual is regarded as an
individual’s health. To keep the body
healthy, every human being, at any age,
needs to have a balanced diet. The
person must also observe personal
hygiene and undertake adequate
physical exercise.
During adolescence, however, these
become even more essential as the body
is growing.
Nutritional Needs of the Adolescents
Adolescence is a stage of rapid growth
and development. Hence the diet for an
Are there hormones in
other animals also? Have
they any role to play in
reproduction?
If people do not have
enough iodine in their diet,
will they get goitre caused
by lack of thyroxine?
Activity 7.3
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adolescent has to be carefully planned.
You have already learnt what a balanced
diet is. Recall that a balanced diet means
that the meals include proteins,
carbohydrates, fats and vitamins in
requisite proportions. Our Indian meal
of roti/rice, dal (pulses) and vegetables
is a balanced meal. Milk is a balanced
food in itself. Fruits also provide
nourishment. For infants, mother’s milk
provides all the nourishment that
they need.
Iron builds blood and iron-rich food
such as leafy vegetables, jaggery, meat,
citrus, Indian gooseberry (amla) are good
for adolescents.
Check items for lunch and dinner in
your meal. Is the meal balanced and
nutritious? Does it include cereals
which give energy and milk, meat, nuts
and pulses which provide proteins for
growth? Also, does it include fats and
sugar that give energy? What about
fruits and vegetables which are
protective foods? Chips and packed or
tinned snacks, though very tasty
should never replace regular meals as
they do not have adequate nutritional
value.
Activity 7.4
Make a group with your friends.
Write down the items of food in your
breakfast, lunch and dinner you
had on the previous day. Identify
the items responsible for proper
growth. Also identified the junk
food that you consumed the
previous day.
Personal Hygiene
Everyone should have a bath at least
once everyday. It is more necessary for
teenagers because the increased activity
of sweat glands sometimes makes the
body smelly. All parts of the body should
be washed and cleaned everyday. If
meat
vegetables
fruits
milk and
eggs
grains
Fig. 7.6 : Nutritious items of food
Activity 7.5
Get ideas from the pictures given in
Fig.7.6. Prepare charts or posters
and paste them in the class so that
you are aware of the diet for
adolescents. You may use your
creative ideas and present it like an
advertisement. You may even
organise a competition on this topic.
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cleanliness is not maintained there are
chances of catching bacterial infection.
Girls should take special care of
cleanliness during the time of menstrual
flow. They should keep track of their
menstrual cycle and be prepared for the
onset of menstruation. Use sanitary
napkin or clean homemade pads.
Change pads after every 4–5 hours as
per the requirement.
Physical exercise
Walking and playing in fresh air keeps
the body fit and healthy. All young boys
and girls should take walks, exercise
and play outdoor games.
Activity 7.6
Collect data on the number of
children in your class who exercise
regularly and who do not exercise
regularly. Did you notice any
difference in their fitness and
health? Prepare a report on the
benefits of regular exercise.
Say “NO” to Drugs
Adolescence is a period of much
activity in the body and mind which
is a normal part of growing up. So do
not feel confused or insecure. If
anybody suggests that you will get
relief if you take some drugs, just say
‘No’ unless prescribed by the doctor.
Drugs are addictive. If you take them
once, you feel like taking them again
and again. They harm the body in the
long run. They ruin health and
happiness.
You must have heard about AIDS
which is caused by a dangerous virus,
HIV. This virus can pass on to a
normal person from an infected
person by sharing the syringes used
for injecting drugs. It can also be
transmitted to an infant from the
infected mother through her milk. The
virus
can also be transmitted through
sexual contact with a person infected
with HIV.
Adolescent Pregnancy
You might be knowing that in our country, the legal age for marriage is 18 years
for girls and 21 years for boys. This is because teenage mothers are not prepared
mentally or physically for motherhood. Early marriage and motherhood cause health
problems in the mother and the child. It also curtails employment opportunities for
the young woman and may cause mental agony as she is not ready for
responsibilities of motherhood.
Myths, Taboos, Do’s and Don’ts
You have learnt here and from Chapter
6 the scientific facts related to human
reproduction. There are many wrong
notions which you should now be able
to discard as informed adolescents. For
example, there are myths and taboos
regarding bodily changes that
adolescents experience. Some of these
are given below and you can now argue
why these are myths and not facts.
1. A girl becomes pregnant if
she looks at boys during
menstruation.
2. The mother is responsible for the
sex of her child.
3. A girl should not be allowed to
work in the kitchen during
menstruation.
You may come across many other myths
and taboos. Discard them.
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KEYWORDS KEYWORDS
KEYWORDS KEYWORDS
KEYWORDS
ADAM’S APPLE
ADOLESCENCE
ADRENALIN
BALANCED DIET
ENDOCRINE GLANDS
ESTROGEN
HORMONES
INSULIN
LARYNX
PITUITARY GLAND
PUBERTY
REPRODUCTIVE
HEALTH
SECONDARY SEXUAL
CHARACTERS
SEX CHROMOSOMES
TARGET SITE
TESTOSTERONE
THYROXINE
VOICE BOX
WHAT YOU HAVE LEARNT WHAT YOU HAVE LEARNT
WHAT YOU HAVE LEARNT WHAT YOU HAVE LEARNT
WHAT YOU HAVE LEARNT
Ü Humans become capable of reproduction
after puberty sets in. Children between the
ages of 11 and 19 years are called adolescents.
Ü The onset of puberty brings about growth of
the reproductive organs. Hair grow at
various places on the body. Breasts develop
in girls and facial hair (moustache and beard)
appear in boys. Voice of boys becomes hoarse
as voice box enlarges during adolescence.
Ü Children gain height during adolescence.
Ü The onset of puberty and maturity of
reproductive parts are controlled by hormones.
Ü Hormones are secretions of endocrine glands
which pour them directly into the blood stream.
Ü Pituitary gland secretes hormones which
include growth hormone and hormones that
make other glands such as the testes, ovaries,
thyroids and adrenals, secrete hormones.
Pancreas secretes insulin, thyroid produces
thyroxine and adrenals produce adrenalin.
Ü Testosterone is the male hormone and
estrogen, the female hormone. The uterine wall
in females prepares itself to receive the
developing fertilised egg. In case there is no
fertilisation, the thickened lining of the uterine
wall breaks down and goes out of the body
along with blood. This is called menstruation.
Ü Sex of the unborn child depends on whether
the zygote has XX or XY chromosomes.
Ü It is important to eat balanced food and
maintain personal hygiene during
adolescence.
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Exercises
1. What is the term used for chemical secretions of endocrine glands
responsible for changes taking place in the body?
2. Define adolescence.
3. What is menstruation? Explain.
4. List changes in the body that take place at puberty.
5. Prepare a Table having two columns depicting names of endocrine glands
and hormones secreted by them.
6. What are sex hormones? Why are they named so? State their function.
7. Choose the correct option.
(a) Adolescents should be careful about what they eat, because
(i) proper diet develops their brains.
(ii) proper diet is needed for the rapid growth taking place in their
body.
(iii) adolescents feel hungry all the time.
(iv) taste buds are well developed in teenagers.
(b) Reproductive age in women starts when their
(i) menstruation starts.
(ii) breasts start developing.
(iii) body weight increases.
(iv) height increases.
(c) The right meal for adolescents consists of
(i) chips, noodles, coke.
(ii) chapati, dal, vegetables.
(iii) rice, noodles and burger.
(iv) vegetable cutlets, chips and lemon drink.
8. Write notes on—
(a) Adam’s apple.
(b) Secondary sexual characters.
(c) Sex determination in the unborn baby.
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9. Word game : Use the clues to work out the words.
Across
3. Protruding voice box in boys
4. Glands without ducts
7. Endocrine gland attached to brain
8. Secretion of endocrine glands
9. Pancreatic hormone
10. Female hormone
Down
1. Male hormone
2. Secretes thyroxine
3. Another term for teenage
5. Hormone reaches here through blood stream
6. Voice box
7. Term for changes at adolescence
E X E R C I S E S
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10. The table below shows the data on likely heights of boys and girls as they
grow in age. Draw graphs showing height and age for both boys and
girls on the same graph paper. What conclusions can be drawn from
these graphs?
Height (cm)
Boys Girls
0 53
53
4 96
92
8 114 110
12 129 133
16 150 150
20 173 165
Age
(Years)
Extended Learning — Activities and Projects
1. Find out from your elder relatives about their awareness of the
legal status of early marriage. You yourself may get information on
it from your teacher, parents, a doctor or the internet. Write a two-
minute speech explaining why early marriage is not good for the
couple.
2. Collect newspaper cuttings and information in magazines about HIV/
AIDS. Write a one page article of 15 to 20 sentences on HIV/AIDS.
3. In our country, according to 2011 census, there are 940 adolescent
females for every 1000 males. Find out.
(a) the concerns of the community regarding this low ratio.
Remember that the chance of having a boy or a girl is equal.
(b) what amniocentesis is and how useful this technique is. Why
is its use for identification of sex of the unborn child banned
in India?
4. Put your ideas together and write a short note on the importance of
knowing facts about reproduction.
For more information visit :
l www.teenshealth.org/teen/sexual_health/
l www.adolescenthealth.com
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